The present invention relates generally to handheld power tools, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools or combustion nailers.
Combustion-powered tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE®, BUILDEX® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or pre-firing position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Conventional combustion fastener driving tools inherently create a resistance to the user pressing the tool against a workpiece before a fastener is driven. This operation causes a main portion of the tool to depend vertically under user pressure against at least one biasing element relative to a workpiece contact element for causing internal operational steps prior to ignition. Such steps include movement of the valve sleeve toward a cylinder head to close the combustion chamber, and the delivery of a dose of fuel from the fuel cell into the closed combustion chamber. In conventional tools, the resistance of the various internal components and linkages in this operation combine to create a significant actuation force. Conventional combustion nailers have an actuation force in the range of 10-14 pounds. The actuation force is sufficient to contribute to user fatigue after periods of extended tool operation.